The present invention relates to shipbuilding and vessel repair, and more particularly, the present invention relates to a rebuilt double hull vessel and method of rebuilding a vessel having an existing single hull into a vessel having a double hull. Even more particularly, the present invention relates to a rebuilt double hull vessel and method of internal double hulling, wherein the existing internal structure and deck of a vessel are cut out and removed from the shell of the existing single hull, a new inner hull is fabricated and installed inside the existing outer hull to form a double hull design, the original internal and deck structure is modified, fitted over, and then coupled to the new inner hull.
The shipping and cargo moving industry is continually faced with customer demands for new and improved vessel designs and for new and improved methods of modifying the design of existing vessels. Substantial cost savings can be realized by a vessel owner in modifying or rebuilding existing vessels to incorporate improvements in vessel designs or otherwise extend the life of the vessel rather than paying the cost of building a new vessel.
In addition, new governmental and environmental regulations place certain restrictions and requirements on vessel owners and operators. These new or required designs must be capable of securely holding a cargo and also of being seaworthy. At the same time, a vessel must comply with shipping and environmental requirements and regulations.
A typical vessel comprises a vessel having a single hull design. This type of hull construction provides a single outer hull or skin that provides structural integrity and acts as a boundary between the operating environment of the vessel (e.g., the sea) and the cargo and internal structure of the vessel. The single hull typically includes a shell having a bottom, a port side, a starboard side, a bow, a stem, and a plurality of transverse and longitudinal bulkheads and internal stiffening frames that support and strengthen the shell of the hull. This internal framing typically comprises a combination of transverse and longitudinal members.
As a result of the recent heightened environmental awareness and several shipping mishaps, new governmental regulations have been implemented requiring the use of double hulls on designated vessels in U.S. waters out to the 200 mile economic zone limit. These double hull requirements are contained in the Oil Pollution Act of 1990 (OPA-90) and have been incorporated in U.S. Coast Guard regulations. In part, OPA-90 requires that all new tank vessels constructed under contracts awarded after 1990 must have double hulls and that all existing single hull vessels engaged in the marine transport of oil and petroleum products be rebuilt with double hulls or be retired between the years 1995 and 2015, depending on the size and age of the vessel.
This has created a great burden on carriers having existing single hull vessels. These single hull vessels will either have to be rebuilt to incorporate a double hull design at great cost to the carrier, or the vessel will have to be retired, in many cases years before the end of its economically useful life.
Double hull designs have been used in the construction of newer vessels in an effort to comply with the requirements of the OPA-90. These double hull vessels typically have an outer hull and an inner hull. The outer hull and the inner hull each have shell plating that forms the structural integrity of the hull. A combination of transverse and longitudinal framing is provided between the inner and the outer hull to help strengthen the shell plating. The idea behind a double hull is that the structural integrity of the outer hull may be breached without breaching the inner hull. Therefore, the outer hull may be breached, i.e., opened to the sea, while the cargo would remain securely contained within the inner hull. Thereby, a potential cargo spill will have been avoided. Typical cargos that have spilled in the past to cause environmental mishaps include cargos such as an oil, a petroleum, a chemical, or other hazardous materials. Of course the provision of a double hull adds to the complexity and cost of new construction. xe2x80x9cMETHOD AND DEVICE FOR THE INSTALLATION OF DOUBLE HULL PROTECTIONxe2x80x9d, U.S. Pat. No. 5,218,919, issued on Jun. 15, 1993, Krulikowski et al. describes the construction of an auxiliary hull, exterior to the primary hull of a ship, which has the capacity to absorb impact energy preventing primary hull puncture, which may be retrofitted to existing single hull ships. However, this external fitting of a new auxiliary hull outside the existing single hull to form a double hull is costly and significantly changes the operational characteristics of the vessel. The breadth and draft of the ship are changed as a result of this external double hulling. This affects the ports that the vessel may access and the port interface characteristics of the vessel. Additionally, as is the case of a vessel with a pushing notch, an external double hulling will change the tugboat interface. External double hulling also affects the wave and wind characteristics of the vessel. In addition, the cargo carrying capabilities of the vessel may be affected, which in turn may affect the customers that may be serviced by a particular vessel.
Therefore a need exists for the rebuild of an existing single hull vessel with a new double hull. Preferably, this double hulling maintains the external shape and dimensions of the outer hull so that the vessel""s hull performance and operational characteristics remain substantially the same.
The present invention is directed to a double hull vessel (particularly a seal going vessel) and a method of internally rebuilding an existing vessel having a single hull design into a vessel having a double hull design. The present invention accomplishes the installation of the new double hull using an internal rebuild concept. The present invention reuses the existing vessel structure to the maximum extent possible, while also maintaining, as much as possible, the cargo carrying and hull operational characteristics of the original vessel. The shape and dimensions of the outer hull of the vessel and the hull performance characteristics of the vessel remain substantially the same, and the existing internal ship structure, including the longitudinal bulkheads, the transverse bulkheads, and top side decking are removed, modified, and reused to the maximum extent possible.
The outer hull of the existing single hull vessel and a new inner hull, which is disposed within a volume defined by the outer hull, define the double hull of the rebuilt vessel. A plurality of framing members are disposed between the inner hull structure and the outer hull and maintain the inner hull in a spaced apart relationship with the outer hull. The new inner hull defines an interior cargo carrying volume and the outer hull defines an exterior of the rebuilt vessel, such that the inner hull provides a boundary in the event that the outer hull is penetrated.
Preferably, the new inner hull structure which forms the new inner hull of the double hull vessel is prefabricated as a plurality of modular sections, and the prefabricated modules are fitted over the top of the existing bottom framing members and joined to the existing framing members at the sides. The prefabricated modules comprise portions of the inner hull plating including the inner bottom plating, port side plating, and starboard side plating, and a plurality of framing members. The framing members include stiffening, members and connecting members. In one preferred embodiment, the connecting members include a plurality of transverse framing members and the stiffening members include a plurality of longitudinal framing members. Alternatively, the connecting membersmay include a plurality of longitudinal framing members and the stiffening members may include a plurality of transverse framing members. The connecting members are connected at one end to an exterior surface of the inner hull structure and extending therefrom and are connected at the other end to the outer hull structure.
The new portions of the primary framing members of the modular sections extend from the inner bottom plating a shorter distance than the new portions of the connecting members, thereby forming a gap when the module is installed over the existing framing. This gap helps facilitate fitting up and welding of each modular section to the existing outer hull structure. The removed internal ship structure and topside deck is modified and then reinstalled over the new inner hull after the inner hull has been installed. Thus, the cargo is primarily contained by new steel (the inner hull), and the exterior structure and coating of the original vessel""s hull define the outer hull of the vessel.
Accordingly, a single hull vessel is rebuilt to have a double hull over at least the entire side and bottom within the length of the cargo carrying volume, while substantially maintaining the major outer hull exterior dimensions and hull hydrodynamic characteristics of the original single hull vessel.
In accordance with a further aspect of the present invention, a new trunk structure is disposed over the opening formed in the topside deck plating when the cut out section of deck plating was removed. The trunk structure includes topside deck (main deck) plating, preferably the existing decking that was cut and removed, and new bulkheads, extending down therefrom. The trunk bulkheads are formed between the cut in the original main deck, in the area where the original topside deck plating and bulkheads were raised to maintain cargo carrying capacity. Preferably, where a new trunk structure is employed, new bulkhead portions are connected to the existing longitudinal and transverse bulkheads to form rebuilt bulkheads. These bulkhead portions are preferably formed as lower bulkhead portions proximate the inner hull to strengthen the rebuilt bulkheads and to provide additional support and strength for the new raised deck and trunk structure. Preferably, new lower portions of the transverse and longitudinal bulkhead are formed extending upward from an inner surface of the new inner hull plating. The trunk structure may be sized to increase or decrease the cargo carrying capacity.
Additional features of the present invention are set forth below.